<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>用户注册</title>
    <script src="js/jquery-3.3.1.min.js"></script>
</head>
<body>
<form autocomplete="off">
    姓名：<input type="text" id="username">
    <span id="uSpan"></span>
    <br>
    密码：<input type="password" id="password">
    <br>
    <input type="submit" value="注册">
</form>
</body>
<script>
    document.getElementById("username").onblur = function () {
        let xmlHttp = new XMLHttpRequest();
        let username = document.getElementById("username").value;
        xmlHttp.open("get", "userServlet?username=" + username, true);
        xmlHttp.send();
        xmlHttp.onreadystatechange = function () {
            if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
                document.getElementById("uSpan").innerHTML = xmlHttp.responseText;
            }
        }
    }
</script>
</html>